1. Field of the Invention
The present invention relates to a direct communication method between slave units and a PHS (Personal Handy-Phone System) terminal for direct communication between PHS slave units. More particularly, the present invention relates to a direct communication method between slave units and a PHS terminal for direct communication between PHS slave units advantageously applicable to data communication between a client and a server.
2. Description of the Background Art
PHS allows a cordless phone to be used both inside and outside of a building. Today, data communication services implementing data communication between PHS slave units to which computers or similar data equipment are connected are spreading. Further, PHS slave units are capable of directly communicating with each other without the intermediary of master units.
To allow two PHS slave units to interchange data by direct communication, it has been customary for each of the slave units to transmit one slot for a frame and then receive one slot for a frame and to interchange data at the same rate as each other. This kind of data communication accords to, e.g., RCR STD-28 which is a PHS standard (Second Generation Cordless Phone System Standard, First Edition) prescribed by ARIB (Association of Radio Industries and Business).
In accordance with the above standard, 5 ms long TDMA (Time Division Multiple Access) frames each are divided into eight so as to allocate four channels to each of an up-link and a down-link. On each of the up-link and down-link, one of the four channels is used as a control slot while the other three channels are used as communication slots. Communication can therefore be held via up to three channels at the same time. The maximum communication rate is 32 kbps for a channel.
However, the conventional technology described above has a problem ascribable to the fact that the up-link and down-link have the same transmission rate, as follows. When the up-link and down-link are noticeably different in the quantity of data to send, transmission efficiency is lowered. For example, assume that a file server or similar data equipment is connected to one PHS slave unit while client""s data equipment is connected to the other PHS slave unit, and that file transfer or similar data communication is held between the two slave units. Then, file transfer from the server to the client is predominant, lowering the total transmission efficiency of the system including the up-link and down-link. Further, when files include, e.g., pictures represented by a great quantity of data, it is desirable to further increase the transfer rate in order to reduce the communication time.
It is therefore an object of the present invention to provide a direct communication method between slave units capable of increasing the transmission rate of at least one of an up-link and a down-link to thereby effect asymmetrical data communication which increases the total transmission efficiency of a system when quantities of data on the up-link and down-link increase, and a PHS terminal having such a capability.
In accordance with the present invention, a method of allowing two PHS slave units respectively connected to two data equipment for data communication to directly communicate with each other via radio channels of TDMA frames begins with the step of connecting one data equipment functioning as a server for data communication to one PHS slave unit, and connecting the other data equipment functioning as a client to the other PHS slave unit. The PHS slave unit of the server is caused to originate a call addressed to the PHS slave unit of the client via a desired communication channel and thereby sets up synchronization between the PHS slave units with respect to an up-link and a down-link via the communication channel. Among m communication slots of a TDMA frame, n (natural number of 1 to m) consecutive communication slots continuing from a slot of the communication channel used for synchronization is set on at least the down-link extending from one of the PHS slave units to the other PHS slave unit. The PHS slave terminals are caused to interchange data at asymmetrical rates with respect to the up-link and the down-link in respective TDMA frames by respectively using some of the n slots and some of (mxe2x88x92n) slots.
Also, in accordance with the present invention, a PHS terminal has a PHS slave unit and data equipment connected to the PHS slave unit for data communication. The PHS terminal includes a continuous slot forming circuit for continuously forming, at least at the time of direct communication between the PHS slave unit and the other PHS slave unit, a desired number of consecutive slots in a TDMA frame. An identification message forming circuit forms, when the PHS terminal calls the other PHS terminal including the other PHS slave unit, a message for informing the other PHS terminal of whether the PHS terminal to which the circuit belongs is a server or a client. A callback control circuit automatically redials if the message shows that the other PHS terminal originated a call is a client. A reserve message forming circuit forms, based on the quantity of data to send, a reserve message representative of the number of slots to reserve in one frame. A number-of-slot setting circuit compares, on receiving the reserve message, the number of reserve slots represented by the reserve message and the number of reserve slots of the PHS terminal to which the circuit belongs, and sets, based on the result of comparison, the number of slots to be sent from the PHS terminal for a frame in the continuous slot forming circuit.